My copending application Ser. No. 867,217 filed Jan. 6, 1978 (continuation of application Ser. No. 766,352 filed Feb. 7, 1977) relates to magnetic-technical systems useful in magnetic separators for separating magnetic materials from liquid or dry materials containing magnetic particles. The magnetic-technical systems are characterized by possessing one magnetic circuit comprising at least two magnets and at least one operating air gap, and being further characterized by the fact that the circuit containing the magnets is closed and that within said circuit there is an operating gap in relation to two mild iron or steel parts which in each case are arranged between two interconnected homopolar magnets.
The present invention relates to a friction gear permanent magnetic entrainment means for rolling transmission of motion in combination with the magnetic-technical system as defined in my forementioned application Ser. No. 867,217.
Mechanically effective friction gears have been known for the most different purposes for years (see LUEGER, "Lexikon der Technik", 4th edition, 1960, vol, 1, pp. 416 to 418).
Magnetic friction gears have profited from the principles and constructional features of the known mechanical friction gears. While the friction efficiency of simple friction gears with magnetic adhesion was fairly satisfactory, strong fields appeared at the magnetic operating air gap (edge effect) besides diminishing magnetic fields, due to the forming of different magnetic potential areas. This occurs for instance in case of friction gears with magnetic contact pressure where the magnets on the one hand partly surround the friction wheels with an air gap and are on the other hand connected to one another by a short-circuit element as disclosed in my German Pat. No. 10 59 734. Due to these air gaps the magnetic circuit is not completely closed. This is due to the fact that nonuniform magnetic potential areas occur at the free poles of the permanent magnets and at the induced friction gears. As a result this leads to increased ferromagnetic wear which may entail a blocking of the friction gear.
In the application Ser. No. 867,217 a magnetic-technical system having one magnetic circuit comprising at least two magnets and at least one operating air gap has been proposed characterized by a frame being composed of symmetrically arranged permanent magnets and symmetrically arranged mild iron or steel parts with the mild iron or steel parts arranged between analogous poles of the magnets forming central frontal surfaces drawn into the interior of the frame, which central frontal surfaces are opposing one another forming an operating air gap with opposite polarities in the direction of magnetizing. With such a closed circuit the lines of force are concentrated to the and in the operating air gap in a practically completely homogenically magnetized way so that the outer stray fields are kept small and magnetic dispersions within the yoke as well as outside the effective area are widely avoided.
As compared to known magnetic systems, a system with considerably less dispersion is reached largely preventing outer stray and producing a stronger homogenic magnetic field in the operating air gap.
The present invention proposes the application of that new magnetic-technical system to friction gears with permanent magnetic entrainment or adhesion, resulting in the fact that nonuniform magnetic potential areas are avoided at the free poles of the permanent magnets and at the induced friction wheels of the friction rollers. As thus for instance rotating friction wheels placed in a common frame and pivoted on adjustable axes can produce oppositely polarized parts of a magnetic circuit closing the magnetic system, it is possible to arrange outside the frame block magnets with pole shoes of practically unlimited size and thus to achieve adhesive forces also with larger gaps for the entrainment of the friction wheels, having been regarded as inachievable until now.